|Publication number||US5671221 A|
|Application number||US 08/490,193|
|Publication date||Sep 23, 1997|
|Filing date||Jun 14, 1995|
|Priority date||Jun 14, 1995|
|Also published as||EP0749215A2, EP0749215A3|
|Publication number||08490193, 490193, US 5671221 A, US 5671221A, US-A-5671221, US5671221 A, US5671221A|
|Original Assignee||Sharp Microelectronics Technology, Inc., Sharp Kabushiki Kaisha|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (15), Non-Patent Citations (30), Referenced by (107), Classifications (12), Legal Events (6)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present invention relates generally to communication, and more particularly, to a spread-spectrum receiver method and apparatus usable in connection with a direct sequence (DS) code division multiple access (CDMA) communication system.
Although CDMA communication systems still are relatively new, it is apparent that such systems represent a significant improvement in communication technology, particularly in view of the ever-increasing requirements for user capacity, signal accuracy, and message security. This improvement is nowhere more apparent than in a wireless communication system such as a digital cellular telephone system whereby a number of users, or subscribers, communicate from within defined geographic areas, or cells. In such a system, each cell includes a base station, or cell site, which controls communication between in-cell users, nonsystem users and other cell sites.
In a conventional CDMA digital cellular telephone system, there are two links over the air from a subscriber unit (i.e., a cellular phone or handset) to a cell site, and from the cell site to the subscriber unit. For the first link, i.e. from the subscriber unit to the cell site, an analog voice signal is picked up at the subscriber unit where it is processed and fed to a vocoder which transforms the processed signal into a digital information bit stream. Typically, the vocoder takes advantage of the idiosyncracies of human speech to vary the rate at which it converts the signal to digital information bits (e.g., it need only sample a pause or other dead space at a very low rate). The information bits are framed, convolution encoded and interleaved, and then are multiplied by a unique user code sequence which effectively spreads the spectrum in a highly controlled, but apparently random, way. The spread signal is modulated onto a radio frequency carrier for transmission to the cell site.
The cell site receives the signal transmitted by the intended subscriber unit, along with signals from all other in-cell users, and feeds them to a series of receivers where such signals are demodulated and de-spread. Each receiver thus is left with only the original voice information bits from the corresponding user. These information bits then are used to produce a facsimile of the original speech. The information bits are again framed, convolution encoded, interleaved and spread, for the second link, i.e. cell site to subscriber unit, of the cell site this time according to the intended subscriber unit's user code sequence. The signal is modulated onto the radio frequency carrier of the sending cell site. A power control system typically is used to keep the RF output of each phone to a minimum, thereby decreasing interference between cells.
Considering now a typical spread-spectrum receiver of a CDMA digital cellular telephone system, it will be understood that a signal r(k), which is the signal incident upon the spread-spectrum receiver at discrete time k (the time interval for k is a sample interval Tcs, which may be the same as chip interval Tc, or a fraction of the chip interval), may be described by the equation:
r(k)=s(k) h(t,τ)+sp (k) h(t,τ)+io (k) h(t,τ)+Ioc (k)
where s(k) is a coded source signal sent to the intended receiver, sp,(k) is a PILOT channel signal, and io (k) is same-cell interference (including other user source signals, interferences and artifacts from the PAGE and SYNC channels). h(t,τ) is a same-cell multipath fading channel model, which may be expressed in accordance with the equation: ##EQU1## where cj (t) is a weighting factor for multipath component j, δ(t-τj) is a delta function, and m is the total number of multipath components. t represents time. τ is the time delay spread. Ioc (k) includes both other-cell interference and thermal noise and may be expressed as: ##EQU2## where sj (k) is a coded source signal of other-cell j, hj (t,τ) is a multipath fading channel model of the other-cell and no (k) is thermal noise. u represents the total number of other cells which contribute to Ioc (k). Received signal r(k) is shown diagrammatically in FIG. 1.
It will be appreciated that only the signal components which are specifically to be sent to the intended receiver are coded with the intended receiver's user code sequence and frequency. All others are coded with other code sequences, other frequencies, or are not coded at all. Interference, including interference from other users, noise and other artifacts, thus effectively may be reduced relative to the intended signal because such interference is relatively uncorrelated with a given user code sequence and frequency while the intended signal is relatively highly correlated with such user code sequence and frequency. It will be understood, however, that achieving the highest cost-effective performance requires a high degree of correlation between the received information and the transmitted information, but it does not require, and typically does not achieve, complete correlation.
Use of the terms correlated and correlation herein will be understood to be relative rather than absolute. Thus, a relatively high correlation between codes, sequences, waveforms or signals may be referred to as a correlation. Conversely, codes, sequences, waveforms or signals with a relatively low correlation therebetween may be referred to as being uncorrelated. User code sequences sometimes are referred to as being nearly orthogonal, meaning that they have little cross-correlation with one another.
It will be appreciated by those skilled in the art that CDMA communication takes advantage of spatial diversity, frequency diversity and time diversity (which of course is related by distance to spatial diversity). In conventional CDMA communication systems rake receivers have been used to utilize time diversity, such receivers being convenient because they are capable of collecting signal energy from various received signal paths that fall within the span of delayed time intervals and carry the same user code sequence. A conventional rake receiver will be understood to include plural samplers, a weighted summer and a decision circuit. Such rake receivers have been shown to provide a practical, robust solution for multipath fading in cellular telephone communication systems.
U.S. Pat. No. 5,081,643 entitled SPREAD SPECTRUM MULTIPATH RECEIVER APPARATUS AND METHOD, which issued Jan. 14, 1992, describes apparatus for adapting a receiver to identify the path having the greatest amplitude in a spread-spectrum signal characterized by multipath components. A first correlator correlates the spread-spectrum signal received at the input with a chip code signal representing a first time delay. A second correlator correlates the spread-spectrum signal received at the input with a chip code signal representing a second time delay. A comparator generates first and second time delay indicator signals by comparing the outputs of the two correlators.
U.S. Pat. No. 5,103,459 entitled SYSTEM AND METHOD FOR GENERATING SIGNAL WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM, which issued Apr. 7, 1992, describes a communication system and method for use in a CDMA cellular telephone system in which signals are communicated from a cell-site to a mobile unit using direct-sequence, spread-spectrum techniques. Pilot, synchronization, paging and voice channels are defined by encoding, interleaving, bi-phase shift key modulating with orthogonal covering of each symbol, along with quadrature phase shift key spreading of the covered symbols.
U.S. Pat. No. 5,109,390 entitled DIVERSITY RECEIVER IN A CDMA CELLULAR TELEPHONE SYSTEM, which issued Apr. 28, 1992, describes a diversity receiver for use in a CDMA cellular telephone system in which PN processing gain and time discrimination properties of such coding are used to determine the location in the time domain and the received signal strength of the received pilot signal for each of multiple paths. A searcher receiver provides a control signal indicative of the received pilot signals of greatest strength and their corresponding time relationship. A data receiver receives spread-spectrum communication signals accompanying such received pilot signals and, responsive to the searcher control signal, acquires and demodulates a spread-spectrum communication signal that corresponds to the pilot signal of greatest signal strength.
Finally, U.S. Pat. No. 5,228,056 entitled SYNCHRONOUS SPREAD-SPECTRUM COMMUNICATIONS SYSTEM AND METHOD, which issued Jul. 13, 1993, describes a synchronous spread-spectrum communications system and method in which a combiner combines a chip code signal with a spread-spectrum processed signal and in which a receiver message mixer despreads the spread-spectrum communications signal as a modulated data signal. Synchronization relies on a tracking and acquisition circuit that uses a recovered carrier signal produced by the spread-spectrum communications signal transmitter.
The use of CDMA communication is expected to significantly increase capacity in cellular telephone systems by increasing the signal-to-noise ratio (SNR) within each channel so as to improve the receiver's ability within the channel to differentiate between an intended receiver's source signal and noise (including interference made up of transmissions not intended for the given receiver and thermal noise). Nevertheless, practical problems have arisen in CDMA rake receiver field deployment. These problems include propagation path loss, time delay spread, external interference, geographic distribution and the relationship between diversity gain and self-interference due to uncaptured energy within an arm of the rake receiver. Such problems have resulted in CDMA capacity reductions and voice quality degradation.
Briefly, the present invention involves a receiving apparatus for use in a communication system wherein a spread-spectrum signal is transmitted within an environment tending to produce multipath fading. The receiving apparatus includes a channel estimator which estimates channel coefficients, such coefficients preferably corresponding to the level of correlation between various multipath components of the spread-spectrum signal and a cell-correlation signal. A channel selector is configured to select one or more of the multipath components based on the channel coefficients, typically choosing multipath components with the greatest level of correlation which is indicative of a high signal-to-noise power ratio. The channel selector also identifies time delay values representing the time delay between such selected multipath components, the time delay values being used by a spread-spectrum receiver to identify the selected multipath components for presentation on diversity branches. A combiner combines the diversity branches in a predetermined manner, typically by weighted summation using weighting factors produced by the channel selector. A decoder extracts information from the combined signal and outputs the information which is used to produce synthesized speech.
The invention also involves a receiving method for use in a communication system, the method typically involving: 1) receiving a spread-spectrum signal having multipath components; 2) selecting one or more of such multipath components based on predetermined selection criteria; 3) determining time delays between the selected multipath components; 4) determining weighting factors for the selected multipath components; 5) processing the spread-spectrum signal by operation thereon by selected time-delayed versions of a user-correlation signal to produce processed signal components; 6) integrating each processed signal component during a predefined time period to produce corresponding integration results; 7) weighting the integration results using the weighting factors; 8) summing the weighted integration results to produce a summed output; and 9) decoding the summed output by quantizing such output and comparing such output to a predefined threshold value, thereby to extract information from the summed output. The processing step may include multiplying the spread-spectrum signal by a user-correlation signal in the form of a user code sequence which is defined by multiplication of a pseudo-random number (PN) sequence and an orthogonal cover sequence, or alternatively, by modulo-2 adding the PN sequence and the orthogonal cover sequence.
The channel estimator and channel selector typically are embodied by a search engine which identifies the multipath components having the highest level of correlation to the PN sequence. As a result, the invented apparatus exhibits an increased signal-to-noise ratio and quickly adapts to variable diversity paths that are characteristic of mobile wireless communications. By combining weighted outputs the method maximizes diversity gain. Thus, the invention addresses the time delay spread and self-interference due to uncaptured energy problems that characterize conventional rake receiver approaches in CDMA communications.
These and additional objects and advantages of the present invention will be more readily understood after consideration of the drawings and the detailed description of the preferred embodiment.
FIG. 1 is a block diagram which illustrates signal and noise factors that bear on a spread-spectrum receiver apparatus.
FIG. 2 illustrates a prior art rake receiver circuit used in spread-spectrum signal reception.
FIG. 3 is a block diagram of a receiver apparatus constructed in accordance with a preferred embodiment of the present invention.
FIG. 4 is a schematic diagram of a search engine including a channel estimator and channel selector for use in the receiver apparatus shown in FIG. 3.
FIG. 4A is a schematic diagram of an alternative embodiment of the search engine which forms a part of the receiver apparatus of FIG. 3.
FIG. 5 is a schematic diagram of a rake receiver and combiner of the receiver apparatus shown in FIG. 3.
FIG. 6 is a graphical illustration of a comparison between the frame error rate (FER) v. the bit-energy-to-noise-density ratio (Eb /No) for prior art receivers and for the invented receiver apparatus.
In a typical spread-spectrum signal of a CDMA cellular telephone system as diagrammed, it will be understood that a desired source signal s(k) will be corrupted by effects from a variety of sources, including a PILOT channel artifact, interference from other users (both within the same cell and from other cells), mobile channel fading, and thermal noise. These effects add to the desired source signal, producing a received signal which is significantly different from that sent. FIG. 1 shows a typical received signal r(k) which is made up of the desired source signal s(k), the PILOT channel signal sp (k), same-cell interference io (k), other-cell interference and thermal noise.
As indicated, same-cell interference io (k) includes the source signals of all other in-cell users, the SYNC channel signal, and the PAGE channel signal. Other-cell interference Ioc (k) includes the source signals from all other cells (identified as s1 (k), s2 (k), . . . su (k)), along with thermal noise no (k). All in-cell signals pass through a fading multipath channel characterized by the channel model h(t,τ). The source signals sent by other-cell users pass through fading multipath channels corresponding to their respective cell sites. In FIG. 1, the fading multipath channels of the other cells are represented by channel models h1 (t,τ), h2 (t,τ), . . . hu (t,τ) which correspond to source signals s1 (k), s2 (k), . . . su (k), respectively. Received signal r(k) thus contains both a desired, or intended, source signal component, and various undesired signal components including interference and thermal noise. It is, however, only the desired source signal s(k) which contains the information that defines the intended speech.
Turning now to FIG. 2, an idealized prior art rake receiver is shown in block diagram form, such receiver including a plurality of data receiver arms (represented in FIG. 2 as time-delaying buffer gates, each characterized as imposing a 1/Wss time delay). The data receiver arms are suggestive of a rake's fines, the arms being cascaded such that they present incrementally time-delayed versions of a received signal y(t). It thus will be appreciated that their individual diversity components may be expressed as y(t+(j/Wss)) where t is time and j=1, 2, . . . L for an L-branch rake receiver. Each diversity component is multiplied by a predefined transfer function Aj (t)φ(t,θj), and the resultant products are summed, or integrated, over time interval T (corresponding to the system's symbol rate) to produce output rprior (t). The output of the rake receiver of FIG. 2 thus approximates the transmitted signal at the transmission site.
In contrast, the invented receiver apparatus is shown at 10 in FIG. 3, such apparatus taking the form of a mobile receiver unit for use in a CDMA digital cellular telephone system. As indicated, apparatus 10 includes a rake receiver 12 having L receiver arms 12a, 12b, . . . 12L (also known as diversity branches), all of which receive a received signal, designated r(k). The receiver arms also receive a common user-correlation signal in the form of a unique user code sequence defined by multiplication of a PN sequence by an orthogonal cover sequence, so designated. Time delays are imposed upon receiver arms 12a, 12b, . . . 12L by a search engine 14.
In the preferred embodiment, search engine 14 includes a channel estimator 22 which considers a first quantity of multipath components, and a channel selector 24 which selects a second lesser quantity of multipath components for presentation on the rake receiver's receiver arms. The channel estimator estimates correlation between a cell-correlation signal and the various multipath components. The channel selector selects those components with the greatest correlation and adapts the rake receiver for presentation of such selected components on the receiver arms. The outputs of the receiver arms thus represent various selected multipath components of the desired source signal s(k), such components having been extracted from the received signal r(k).
The outputs of the receiver arms are input to a diversity combiner 16, which also receives weighting factors from the search engine to enable the combiner to produce a weighted sum of its diverse inputs. The output of combiner 16, in turn, is input to a normalizer/quantizer 18, which scales and shifts the input to within a predefined range. The output of normalizer/quantizer 18 is decoded by a soft Viterbi decoder 20, the output of such decoder representing the received information that was initially contained within the source signal s(k).
Turning next to FIG. 4, where channel estimator 22 is shown in greater detail, it will be noted that such channel estimator determines a channel coefficient for each of N multipath components. This is accomplished using a time delay arrangement 30 including a plurality of time delays 30a, 30b, 30c, . . . 30N-1, which cream successively time-delayed versions of the channel estimator's cell-correlation signal (which, in the depicted embodiment, is the PN sequence). In the depicted embodiment, each version of the cell-correlation signal is delayed a first predetermined time Tcs (represented by Z-1 in FIG. 4) relative to the next-previous correlation signal version, time Tcs generally being chosen in accordance with the system's chip interval.
The received signal is considered within the channel estimator by operation of a processor arrangement (indicated generally at 32) which multiplies the received signal by the successively time-delayed versions of the cell-correlation signal. Processor arrangement 32, it will be noted, includes a series of multipliers 32a, 32b, 32c, 32d, . . . 32N, each of which multiplies a version of the cell-correlation signal by the received signal to produce a corresponding multipath correlation component. Each multipath correlation component is integrated over a second predefined interval of time (i.e., a symbol interval) by an integrator arrangement 34 which includes a plurality of integrators, or summers 34a, 34b, 34c, 34d, . . . 34N. Each integrator operates to produce a channel coefficient corresponding to the level of correlation over the second predefined interval of time (i.e., a symbol interval T).
The channel estimator thus will be understood to provide estimated channel coefficients cj (i) at discrete time i (where the time interval for i is the symbol interval T) in accordance with the equation: ##EQU3## where Kc is a constant, τj is the indexed time delay shift of multipath component j, w* pilot (k-τj) is the orthogonal spread waveform for the pilot channel, and p* (k-τj) is the PN sequence for the user's cell site, as acquired from the pilot channel. In accordance with the TIA/EIA/IS-95 standard, w* pilot (k-τj)=-1. Channel estimator 22 thus may be considered to estimate correlation between the received signal and the PN sequence simply by multiplication of the PN sequence and the received signal, and summation (or integration) of such product over a predetermined time interval.
As indicated, the channel estimator outputs the channel coefficients to channel selector 24, which selects the multipath components having the greatest level of correlation (i.e., the greatest signal-to-noise power ratios as determined by a sliding, or running average approach). This sliding average is estimated by a fixed length block average, where the block is moving along the time axis at a symbol rate. The selected multipath components are identified by the time delay between such selected multipath components which are represented by time delay values τ1, τ2, . . . τL as output by channel selector 24. The time delay values are updated at a rate which is sufficiently low to avoid excessive cross-correlation error, but sufficiently high to track temporal variations in the multipath components. The time delay values are output to the rake receiver arms, which utilize such values to identify the L maximal correlation multipath components for presentation on diversity receiver arms 12a, 12b, . . . 12L. The channel selector also outputs estimated weighting factors c1 *, c2 *, . . . cL * which typically are complex conjugates of corresponding channel coefficient inputs. The weighting factors are output to diversity combiner 16 for use in providing a weighted sum of the selected multipath components as will described below.
Referring now briefly to FIG. 4A, which represents an alternative embodiment of the invented search engine, it will be seen that the previously described search engine 14 may be replaced by an adaptive search engine 114 which includes a delay value generator in the form of slope signal generator 126 which is capable of producing successive (generally increasing) time delay values x. The time delay values are output to a variable time delay 130 which also receives a cell-correlation signal in the form of a PN sequence. Time delay 130 thus is configured to produce successive time-delayed versions of the cell-correlation signal at time delay intervals which change with time delay value x.
The time delayed versions of the cell-correlation signal are output to a processor arrangement 132, which receives the spread-spectrum signal, and processes such signal by multiplication with the present time-delayed version of the cell-correlation signal. This operation produces a multipath correlation component which is passed to an integrator, or summer, 134 for integration of the multipath correlation component over a predefined interval of time. This occurs for each successive time interval, integration preferably being performed in accordance with a trapezoidal rule which is well known in the art. The resultant product of each integration is a channel coefficient which is passed on to a tracking engine 124.
The tracking engine tracks a predefined number (L) of maximal channel coefficients which are produced by the integrator, and determines corresponding weighting factors for use by diversity combiner 16. With each weighting factor, the tracking engine will receive a corresponding time delay value x from slope signal generator 126. The tracking engine thus selects the multipath components having maximal correlation (as defined by the channel coefficients), and identifies such multipath components using corresponding time delay values received from slope signal generator 126.
Turning now to FIG. 5, rake receiver 12 and diversity combiner 16 will be described in greater detail. As indicated, rake receiver 12 serves to present selected multipath components on plural receiver arms (or diversity branches) 12a, 12b, . . . 12L for weighted combination by combiner 16 to produce a signal which may then be normalized, quantized and decoded. Each receiver arm of rake receiver 12 has an output signal that may be described by the following equation: ##EQU4## where Re denotes the real part of the bracketed complex number, w* user (k) refers to the user's orthogonal cover sequence and L is the total number of rake receiver arms. r(k) is the received signal, p* (k-τj) is the PN sequence. Combiner 16 thus combines the outputs of L rake receiver arms in a predetermined manner. The multipath components presented on the rake receiver arms correspond to the multipath components with the L largest values of channel coefficient amplitudes as defined by τ1, τ2, . . . τL which are received from the channel selector. This may be expressed by the following equation: ##EQU5## where ym (i) is the weighted sum of the selected multipath components for symbol i. The combiner thus will be understood to operate at the symbol rate, each new symbol having a new summed output based on newly selected multipath components as previously described.
Focussing more particularly on the receiver arms, it will be noted that each receiver arm includes a variable time delay 40a, 40b, . . . 40L which receives a time delay value input (τ1, τ2, . . . τL) from channel selector 24. As indicated, the time delays each operate on a user-correlation signal which takes the form of a unique user code sequence (defined by multiplication (or modulo-2 addition) of the PN sequence and the orthogonal cover sequence as indicated) to produce time-delayed versions of the user-correlation signal. The time-delayed versions of the user-correlation signal are received by processors 42a, 42b, . . . 42L, where each time-delayed version of the user-correlation signal is multiplied by the received signal to produce a corresponding processed signal. The processed signals each are integrated via integrators, or summers, 44a, 44b, . . . 44L, which integrate the processed signals over the second predefined time interval (i.e., the symbol interval) so as to produce integration results. The integration result of each receiver arm is then passed to the combiner where it is multiplied (using multipliers 50a, 50b, . . . 50L) by a corresponding weight factor c1 *, c2 *, . . . cL * (from selector 24) to produce corresponding weighted products. The weighted products are then summed using summers (52a, . . . 52L-1) to produce a summed output, or combined signal for passage to normalizer/quantizer 18.
In some implementations, the information bit rate may include voice information that has been convolution-encoded. In such case, a Viterbi decoder may be used to perform convolution decoding. (If such information is not convolution encoded, then no Viterbi decoder is needed.) The decision variable is a normalized combiner output that is adjusted to the input data range of Viterbi soft decoder 20. The decision variable may be expressed as follows: ##EQU6## where Re denotes the real part of the bracketed complex number, and Ku is the input data range for soft decoder quantilization.
Turning finally to FIG. 6, the advantages of the invented receiving method and apparatus are illustrated graphically. The frame error rate (FER), as a ratio, is plotted along the ordinate and the bit-energy-to-thermal-noise-density ratio Eb /No (in decibels) is plotted along the abscissa, for three differently configured receiving systems. In each case, the pilot channel transmitted power is set to 0.2 and each user's channel transmitted power is set to 0.8/63 (where 63 is the maximum number of users in a cell), and a simulated mobile unit speed (as though it were in a speeding vehicle) is at 100 kilometers/hour (100 km/hr). The segmented line connecting solid or filled squares represents a classic five-arm rake receiver system, without normalization. The segmented line connecting blank or outline squares represents a classic five-arm rake receiver system, with normalization. Finally, the segmented line connecting solid or filled diamonds represents a selected three-arm rake receiver system (N=5, L=3), with normalization, i.e., one made in accordance with the invention. It will be appreciated that the illustrated results are achievable in accordance with the preferred embodiment of the invention, although of course better results may be possible with alternative embodiments nevertheless within the spirit and scope of the invention.
It may be seen from FIG. 6 that simply normalizing the output of the combiner improves (lowers) the FER at all pertinent decibel levels. It may also be seen that, by normalizing the output of a selected-arm receiver system such as that described herein as having an adaptive search engine, the FER may be reduced significantly and nearly to the level of the five-arm, normalized system. Thus, with fewer receiver arms, nevertheless the selected and normalized three-arm receiver system achieves nearly the performance of a normalized five-arm system, but with less complexity and cost. With fewer receiver arms, moreover the selected and normalized three-arm receiver system achieves better performance than a conventional non-normalized five-arm system. Stated another way, to achieve FER<0.01, a normalized five-arm receiver system needs 1 db less Eb /No than a non-normalized five-arm receiver system, and a selected, normalized three-arm receiver system needs 0.5 db less Eb /No than a non-normalized five-arm receiver system.
Those of skill in the art will appreciate that the above improvements are only illustrative of the many advantages of the invention, and are not in any way a limitation on the scope of the invention as it is defined by the claims. More and less significant improvements in spread-spectrum cellular telephone systems are achievable by, and are within the spirit and scope of, the invention. It will be appreciated then that the invented method and apparatus provide a performance and cost advantage over conventional rake receiver systems that do not normalize the combiner's output, or that do not select those rake receiver arms exhibiting the highest magnitude mean values, or that do neither. Acceptable FERs are achieved by the use of either or preferably both selection and normalization, as in accordance with the invention.
Accordingly, while the present invention has been shown and described with reference to the foregoing preferred method and apparatus, it will be apparent to those skilled in the art that other changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined in the appended claims.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US4672658 *||Oct 23, 1986||Jun 9, 1987||At&T Company And At&T Bell Laboratories||Spread spectrum wireless PBX|
|US4901307 *||Oct 17, 1986||Feb 13, 1990||Qualcomm, Inc.||Spread spectrum multiple access communication system using satellite or terrestrial repeaters|
|US5081643 *||Nov 16, 1990||Jan 14, 1992||Scs Mobilecom, Inc.||Spread spectrum multipath receiver apparatus and method|
|US5093840 *||Nov 16, 1990||Mar 3, 1992||Scs Mobilecom, Inc.||Adaptive power control for a spread spectrum transmitter|
|US5103459 *||Jun 25, 1990||Apr 7, 1992||Qualcomm Incorporated||System and method for generating signal waveforms in a cdma cellular telephone system|
|US5109390 *||Nov 7, 1989||Apr 28, 1992||Qualcomm Incorporated||Diversity receiver in a cdma cellular telephone system|
|US5164959 *||Jan 22, 1991||Nov 17, 1992||Hughes Aircraft Company||Digital equalization method and apparatus|
|US5166951 *||May 15, 1991||Nov 24, 1992||Scs Mobilecom, Inc.||High capacity spread spectrum channel|
|US5179571 *||Jul 10, 1991||Jan 12, 1993||Scs Mobilecom, Inc.||Spread spectrum cellular handoff apparatus and method|
|US5179572 *||Jun 17, 1991||Jan 12, 1993||Scs Mobilecom, Inc.||Spread spectrum conference calling system and method|
|US5185762 *||May 15, 1991||Feb 9, 1993||Scs Mobilecom, Inc.||Spread spectrum microwave overlay with notch filter|
|US5228056 *||Dec 14, 1990||Jul 13, 1993||Interdigital Technology Corporation||Synchronous spread-spectrum communications system and method|
|US5412686 *||Sep 17, 1993||May 2, 1995||Motorola Inc.||Method and apparatus for power estimation in a communication system|
|US5420850 *||Mar 1, 1994||May 30, 1995||Ntt Mobile Communications Network, Inc.||Mobile station and cell selecting method for code division multiplex access mobile communication|
|US5442625 *||May 13, 1994||Aug 15, 1995||At&T Ipm Corp||Code division multiple access system providing variable data rate access to a user|
|1||Business Week, "Bolting from the Cellular Herd", Aug. 20, 1990, p. 40.|
|2||*||Business Week, Bolting from the Cellular Herd , Aug. 20, 1990, p. 40.|
|3||Cellular Business, "The Quest for Spectrum Efficiency" by Dan Sweeney, Jun. 1991, pp. 24-36.|
|4||*||Cellular Business, The Quest for Spectrum Efficiency by Dan Sweeney, Jun. 1991, pp. 24 36.|
|5||Communications, "Code Division Multiple Access Beyond the Time Domain" by Fred Baumgartner, Feb. 1990.|
|6||*||Communications, Code Division Multiple Access Beyond the Time Domain by Fred Baumgartner, Feb. 1990.|
|7||Global Communications, "Next Wave of Wireless Devices may be CDMA-Base" by Dr. Irwin M. Jacobs, Sep./Oct. 1991, pp. 36-40.|
|8||*||Global Communications, Next Wave of Wireless Devices may be CDMA Base by Dr. Irwin M. Jacobs, Sep./Oct. 1991, pp. 36 40.|
|9||*||Hewlett Packard Company, Concepts of CDMA by Ken Thompson and Dave Whipple, 1993 Wireless Communications Symposium, pp. 22 23.|
|10||Hewlett-Packard Company, "Concepts of CDMA" by Ken Thompson and Dave Whipple, 1993 Wireless Communications Symposium, pp. 22-23.|
|11||IEEE Transactions on Communications, "Theory of Spread-Spectrum Communications--A Tutorial", vol. Com. 30, No. 5, May 1982, pp. 855-884.|
|12||*||IEEE Transactions on Communications, Theory of Spread Spectrum Communications A Tutorial , vol. Com. 30, No. 5, May 1982, pp. 855 884.|
|13||Industrial Communications, "Nynex Announces CDMA Microcellular System for New York City", Aug. 10, 1990, Washington, D.C., Issue No. 31, pp. 1-2.|
|14||*||Industrial Communications, Nynex Announces CDMA Microcellular System for New York City , Aug. 10, 1990, Washington, D.C., Issue No. 31, pp. 1 2.|
|15||Los Angeles Times, "PacTel Cellular Takes a Gamble on Technology", Business Section, Aug. 26, 1990, pp. D1 and D8.|
|16||*||Los Angeles Times, PacTel Cellular Takes a Gamble on Technology , Business Section, Aug. 26, 1990, pp. D1 and D8.|
|17||Mobile Phone News, "Qualcomm, PacTel Complete First CDMA Mobile Call: Questions are Left Unanswered", Nov. 23, 1989, Washington, D.C., vol. 7, No. 24, pp. 1-3.|
|18||*||Mobile Phone News, Qualcomm, PacTel Complete First CDMA Mobile Call: Questions are Left Unanswered , Nov. 23, 1989, Washington, D.C., vol. 7, No. 24, pp. 1 3.|
|19||Principles of Communication Systems, "Spread Spectrum Modulation" by H. Taub and Dr. Schilling, Chapter Seventeen, pp. 720-749.|
|20||*||Principles of Communication Systems, Spread Spectrum Modulation by H. Taub and Dr. Schilling, Chapter Seventeen, pp. 720 749.|
|21||Proceedings of the IEEE, "Introduction to Spread-Spectrum Antimultipath Techniques and Their Application to Urban Digital Radio", vol. 68, No. 3, Mar. 1980, pp. 328-353.|
|22||*||Proceedings of the IEEE, Introduction to Spread Spectrum Antimultipath Techniques and Their Application to Urban Digital Radio , vol. 68, No. 3, Mar. 1980, pp. 328 353.|
|23||Qualcomm Incorporated, "Most Often Asked Questions about CDMA", Aug. 23, 1991, pp. 1-8.|
|24||*||Qualcomm Incorporated, Most Often Asked Questions about CDMA , Aug. 23, 1991, pp. 1 8.|
|25||Qualcomm, Inc., "CDMA Cellular the Next Generation".|
|26||*||Qualcomm, Inc., CDMA Cellular the Next Generation .|
|27||Radio Commuications Report, "Nynex Taps Test of CDMA System in New York City", Mar. 26, 1990, p. 4.|
|28||*||Radio Commuications Report, Nynex Taps Test of CDMA System in New York City , Mar. 26, 1990, p. 4.|
|29||The Wall Street Journal, "AT&T, 2 Bells Plan to Upgrade Cellular Systems", Aug. 2, 1990, p. B2.|
|30||*||The Wall Street Journal, AT&T, 2 Bells Plan to Upgrade Cellular Systems , Aug. 2, 1990, p. B2.|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US5818866 *||Jul 19, 1996||Oct 6, 1998||Matra Communication||Method of selecting propagation delays retained for receiving messages transmitted by spread spectrum radio communication|
|US5822380 *||Aug 12, 1996||Oct 13, 1998||Ericsson Inc.||Apparatus and method for joint channel estimation|
|US5828694 *||Jul 1, 1996||Oct 27, 1998||Trimble Navigation Limited||Determination of multipath tracking error|
|US5835488 *||May 14, 1996||Nov 10, 1998||Sony Corporation||Pseudo random noise sequence code generator and CDMA radio communication terminal|
|US5881058 *||Nov 25, 1996||Mar 9, 1999||Motorola, Inc.||Method for performing a signal search in a wireless communication system|
|US5907582 *||Aug 11, 1997||May 25, 1999||Orbital Sciences Corporation||System for turbo-coded satellite digital audio broadcasting|
|US5917829 *||Dec 1, 1997||Jun 29, 1999||State Of Israel-Ministry Of Defense, Rafael - Armament Development Authority||Asynchronous CDMA decorrelating detector|
|US5933423 *||Jul 3, 1995||Aug 3, 1999||Nokia Telecommunications Oy||Reception method, and a receiver|
|US5953382 *||Jul 17, 1996||Sep 14, 1999||Asano; Nobuo||CDMA system mobile communication receiver|
|US5956367 *||Apr 4, 1997||Sep 21, 1999||Sk Telecom Co., Ltd||Rake receiving apparatus for direct sequence code division multiple access system|
|US5991294 *||Dec 12, 1996||Nov 23, 1999||Alcatel Alsthom Compagnie Generale D'electricite||Method of establishing a multichannel connection, as well as switching facilities, communications network, and transmit-side and receive-side communications network access facilities|
|US5999579 *||Nov 7, 1996||Dec 7, 1999||Fujitsu Limited||Fading equalizer|
|US6009074 *||Jul 24, 1997||Dec 28, 1999||Sk Telecom Co., Ltd.||CDMA modulation and demodulation method reducing interference and a communication system using the same|
|US6014570 *||Dec 18, 1995||Jan 11, 2000||The Board Of Trustees Of The Leland Stanford Junior University||Efficient radio signal diversity combining using a small set of discrete amplitude and phase weights|
|US6018651 *||Nov 29, 1995||Jan 25, 2000||Motorola, Inc.||Radio subscriber unit having a switched antenna diversity apparatus and method therefor|
|US6023615 *||Nov 29, 1995||Feb 8, 2000||Motorola, Inc.||Method for controlling a diversity receiver apparatus in a radio subscriber unit|
|US6047019 *||Sep 19, 1996||Apr 4, 2000||Futaba Denshi Kogyo K.K.||Receiver for spectrum spread communication system|
|US6047035 *||Jun 15, 1998||Apr 4, 2000||Dspc Israel Ltd.||Method and device for quantizing the input to soft decoders|
|US6058138 *||Jun 6, 1997||May 2, 2000||Fujitsu Limited||Radio reception system providing improved transmission quality|
|US6061387 *||Mar 24, 1999||May 9, 2000||Orbital Sciences Corporation||Method and system for turbo-coded satellite digital audio broadcasting|
|US6157687 *||Jun 15, 1998||Dec 5, 2000||Nec Corporation||Rake receiving system with fingers selectively participating rake synthesis|
|US6226282||Dec 23, 1998||May 1, 2001||Hyundai Electronics Ind. Co., Ltd.||Method of searching reverse traffic channels in a CDMA mobile radio communication system|
|US6229840 *||Mar 4, 1998||May 8, 2001||Nec Corporation||Diversity circuit|
|US6229857 *||Jun 2, 1998||May 8, 2001||Intel Corporation||Adaptive ingress filtering system|
|US6275485 *||Dec 3, 1998||Aug 14, 2001||Qualcomm Inc.||Noise characterization in a wireless communication system|
|US6301292 *||Apr 13, 1999||Oct 9, 2001||Kokusai Electric Co., Ltd.||Despreading circuit|
|US6308054 *||Dec 19, 2000||Oct 23, 2001||Hitachi, Ltd.||Diversity wireless communication method and its wireless communication apparatus|
|US6333953 *||Jul 21, 1997||Dec 25, 2001||Ericsson Inc.||System and methods for selecting an appropriate detection technique in a radiocommunication system|
|US6345078 *||Jul 31, 1997||Feb 5, 2002||Lucent Technologies Inc.||Finger assignment system for a multiple finger receiver and method thereof|
|US6389060 *||Dec 12, 1997||May 14, 2002||Sony Corporation||CDMA receiver|
|US6430166 *||Aug 19, 1999||Aug 6, 2002||Alcatel||Receiver and method for CDMA transmission with enhanced path searcher|
|US6434163 *||Oct 10, 1998||Aug 13, 2002||Agere Systems Guardian Corp.||Transverse correlator structure for a rake receiver|
|US6442193 *||Mar 30, 1999||Aug 27, 2002||Koninklijke Philips Electronics N.V.||Combining sub-chip resolution samples in arms of a spread-spectrum rake receiver|
|US6456830 *||Aug 17, 2001||Sep 24, 2002||Hitachi, Ltd.||Diversity wireless communication method and its wireless communication apparatus|
|US6470000 *||Oct 14, 1998||Oct 22, 2002||Agere Systems Guardian Corp.||Shared correlator system and method for direct-sequence CDMA demodulation|
|US6496534 *||Jun 27, 1997||Dec 17, 2002||Oki Electronic Industry Co., Ltd.||CDMA receiver with weighted interference cancellation|
|US6519451 *||Mar 1, 2000||Feb 11, 2003||Sony Corporation||Receiving method and receiving apparatus|
|US6542483 *||Nov 8, 2000||Apr 1, 2003||Motorola, Inc.||Method and an apparatus for Eb/Nt estimation for forward power control in spread spectrum communications systems|
|US6636557 *||Sep 7, 2001||Oct 21, 2003||Kokusai Electric Co., Ltd.||Despreading circuit|
|US6674740 *||Aug 13, 1999||Jan 6, 2004||France Telecom||Iterative rake receiver and corresponding reception process|
|US6678320 *||Aug 31, 1998||Jan 13, 2004||Qualcomm, Incorporated||Efficient finite impulse response filter implementation for CDMA waveform generation|
|US6690665 *||May 13, 1999||Feb 10, 2004||Samsung Electronics Co., Ltd.||Device and method for mobile station for receiving signals transmitted from a base station|
|US6708041 *||Nov 10, 1998||Mar 16, 2004||Telefonaktiebolaget Lm (Publ)||Base station transmit power control in a CDMA cellular telephone system|
|US6788736 *||Aug 17, 1999||Sep 7, 2004||Sharp Kabushiki Kaisha||Matched filter|
|US6885655 *||Jun 12, 2001||Apr 26, 2005||Qualcomm Incorporation||Noise characterization in a wireless communication system|
|US6888877||Jan 17, 2001||May 3, 2005||Infineon Technologies Ag||CDMA receiver|
|US6895541 *||Jan 28, 2000||May 17, 2005||Intel Corporation||Method and device for quantizing the input to soft decoders|
|US6922434||Apr 30, 2001||Jul 26, 2005||Ericsson Inc.||Apparatus and methods for finger delay selection in RAKE receivers|
|US6938196||Apr 4, 2002||Aug 30, 2005||Flarion Technologies, Inc.||Node processors for use in parity check decoders|
|US6957375||Feb 26, 2004||Oct 18, 2005||Flarion Technologies, Inc.||Method and apparatus for performing low-density parity-check (LDPC) code operations using a multi-level permutation|
|US6961888||Jul 11, 2003||Nov 1, 2005||Flarion Technologies, Inc.||Methods and apparatus for encoding LDPC codes|
|US6980833||Nov 16, 1999||Dec 27, 2005||Matsushita Electric Industrial Co., Ltd.||Radio communication device and transmission antenna switching method|
|US7127659||Aug 2, 2004||Oct 24, 2006||Qualcomm Incorporated||Memory efficient LDPC decoding methods and apparatus|
|US7133853||Jul 24, 2003||Nov 7, 2006||Qualcomm Incorporated||Methods and apparatus for decoding LDPC codes|
|US7216047 *||Jul 2, 2004||May 8, 2007||Mitsubishi Denki Kabushiki Kaisha||Time-delay discriminator|
|US7231557||Aug 8, 2003||Jun 12, 2007||Qualcomm Incorporated||Methods and apparatus for interleaving in a block-coherent communication system|
|US7231577||Aug 7, 2003||Jun 12, 2007||Qualcomm Incorporated||Soft information scaling for iterative decoding|
|US7237171||Jul 5, 2005||Jun 26, 2007||Qualcomm Incorporated||Method and apparatus for performing low-density parity-check (LDPC) code operations using a multi-level permutation|
|US7237181||Jul 16, 2004||Jun 26, 2007||Qualcomm Incorporated||Methods and apparatus for reducing error floors in message passing decoders|
|US7286619 *||Mar 19, 2003||Oct 23, 2007||Kabushiki Kaisha Toshiba||CDM receiver apparatus and rake synthesizer apparatus|
|US7346832||Jul 21, 2004||Mar 18, 2008||Qualcomm Incorporated||LDPC encoding methods and apparatus|
|US7376885||Oct 17, 2006||May 20, 2008||Qualcomm Incorporated||Memory efficient LDPC decoding methods and apparatus|
|US7395490||Jul 21, 2004||Jul 1, 2008||Qualcomm Incorporated||LDPC decoding methods and apparatus|
|US7434145||Apr 1, 2004||Oct 7, 2008||Qualcomm Incorporated||Extracting soft information in a block-coherent communication system|
|US7552097||Jun 16, 2006||Jun 23, 2009||Qualcomm Incorporated||Methods and apparatus for decoding LDPC codes|
|US7627801||Jul 5, 2005||Dec 1, 2009||Qualcomm Incorporated||Methods and apparatus for encoding LDPC codes|
|US7673223||Jul 11, 2005||Mar 2, 2010||Qualcomm Incorporated||Node processors for use in parity check decoders|
|US7769078 *||Oct 6, 2004||Aug 3, 2010||Telefonaktiebolaget Lm Ericsson (Publ)||Apparatus, methods and computer program products for delay selection in a spread-spectrum receiver|
|US7903572 *||Nov 16, 2005||Mar 8, 2011||Samsung Electronics Co., Ltd||Method and apparatus for determining a data rate|
|US7966542||Feb 13, 2007||Jun 21, 2011||Qualcomm Incorporated||Method and apparatus for performing low-density parity-check (LDPC) code operations using a multi-level permutation|
|US8020078||Jun 11, 2007||Sep 13, 2011||Qualcomm Incorporated||Methods and apparatus for reducing error floors in message passing decoders|
|US8125883 *||Mar 19, 2007||Feb 28, 2012||Jocelyn Aulin||OFDM in fast fading channel|
|US8196000||Jun 11, 2007||Jun 5, 2012||Qualcomm Incorporated||Methods and apparatus for interleaving in a block-coherent communication system|
|US8218602||Aug 30, 2010||Jul 10, 2012||Rambus Inc.||Method and apparatus for selectively applying interference cancellation in spread spectrum systems|
|US8462689 *||Dec 22, 2004||Jun 11, 2013||Intel Corporation||Receiver for time division multiplex system without explicit time slot assignment|
|US8533568||Mar 17, 2008||Sep 10, 2013||Qualcomm Incorporated||LDPC encoding methods and apparatus|
|US8595569||May 28, 2008||Nov 26, 2013||Qualcomm Incorporated||LCPC decoding methods and apparatus|
|US8683289||May 28, 2008||Mar 25, 2014||Qualcomm Incorporated||LDPC decoding methods and apparatus|
|US8751902||Nov 17, 2009||Jun 10, 2014||Qualcomm Incorporated||Methods and apparatus for encoding LDPC codes|
|US8948231 *||Mar 31, 2014||Feb 3, 2015||Marvell International Ltd.||Determining timing information in a receiver|
|US20010036150 *||Jun 12, 2001||Nov 1, 2001||Roberto Padovani||Noise characterization in a wireless communication system|
|US20020146044 *||Apr 9, 2001||Oct 10, 2002||Riaz Esmailzadeh||Hybrid single/multiuser interference reduction detector|
|US20040153934 *||Jul 11, 2003||Aug 5, 2004||Hui Jin||Methods and apparatus for encoding LDPC codes|
|US20040157626 *||Feb 9, 2004||Aug 12, 2004||Vincent Park||Paging methods and apparatus|
|US20040168114 *||Aug 7, 2003||Aug 26, 2004||Tom Richardson||Soft information scaling for iterative decoding|
|US20040187129 *||Feb 26, 2004||Sep 23, 2004||Tom Richardson|
|US20040196927 *||Apr 1, 2004||Oct 7, 2004||Hui Jin||Extracting soft information in a block-coherent communication system|
|US20040213332 *||Jan 17, 2001||Oct 28, 2004||Markus Doetsch||Cdma receiver|
|US20040216024 *||Aug 8, 2003||Oct 28, 2004||Hui Jin||Methods and apparatus for interleaving in a block-coherent communication system|
|US20040264554 *||Jul 19, 2004||Dec 30, 2004||Harms Brian K||User terminal parallel searcher|
|US20050033537 *||Jul 2, 2004||Feb 10, 2005||Szajnowski Wieslaw Jerzy||Time-delay discriminator|
|US20050078742 *||Oct 6, 2004||Apr 14, 2005||Douglas Cairns||Apparatus, methods and computer program products for delay selection in a spread-spectrum receiver|
|US20050105547 *||Dec 22, 2004||May 19, 2005||Ipr Licensing, Inc.||Receiver for time division multiplex system without explicit time slot assignment|
|US20050138520 *||Jul 16, 2004||Jun 23, 2005||Tom Richardson||Methods and apparatus for reducing error floors in message passing decoders|
|US20050257124 *||Jul 11, 2005||Nov 17, 2005||Tom Richardson||Node processors for use in parity check decoders|
|US20050258987 *||Jul 5, 2005||Nov 24, 2005||Tom Richardson|
|US20060020868 *||Jul 21, 2004||Jan 26, 2006||Tom Richardson||LDPC decoding methods and apparatus|
|US20060020872 *||Jul 21, 2004||Jan 26, 2006||Tom Richardson||LDPC encoding methods and apparatus|
|CN1323502C *||Jun 19, 2002||Jun 27, 2007||上海贝尔有限公司||WCDMA indicating channel receiver|
|CN100449956C *||Aug 24, 2000||Jan 7, 2009||艾利森公司||Apparatus and method for selection of correlation timing rake receivers|
|CN100582971C||Jul 7, 2004||Jan 20, 2010||三菱电机株式会社||A time-delay discriminator|
|DE10001649A1 *||Jan 17, 2000||Aug 2, 2001||Infineon Technologies Ag||CDMA-Empfänger|
|WO1999063684A1 *||May 26, 1999||Dec 9, 1999||Stanford Telecomm Inc||Adaptive ingress filtering system|
|WO1999066658A1 *||Jun 13, 1999||Dec 23, 1999||Dspc Tech Ltd||Method and device for quantizing the input to soft decoders|
|WO2000030276A1 *||Nov 16, 1999||May 25, 2000||Matsushita Electric Ind Co Ltd||Radio communication device and transmission antenna switching method|
|WO2002037929A2 *||Nov 6, 2001||May 16, 2002||Motorola Inc||A METHOD AND APPARATUS FOR Eb/Nt ESTIMATION FOR FORWARD POWER CONTROL IN SPREAD SPECTRUM COMMUNICATIONS SYSTEMS|
|WO2004028022A1 *||Sep 23, 2003||Apr 1, 2004||Tensorcomm Inc||Method and apparatus for selectively applying interference cancellation in spread spectrum systems|
|U.S. Classification||370/320, 370/441, 375/E01.032, 370/335|
|International Classification||H04L1/02, H04B7/26|
|Cooperative Classification||H04B1/7115, H04B1/7113, H04B1/7117, H04B1/709, H04B1/712|
|Jun 14, 1995||AS||Assignment|
Owner name: SHARP MICROELECTRONICS TECHNOLOGY, INC., WASHINGTO
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:YANG, JIN;REEL/FRAME:007611/0278
Effective date: 19950613
|Feb 12, 1996||AS||Assignment|
Owner name: SHARP KABUSHIKI KAISHA, JAPAN
Free format text: CORPORATE TO CORPORATE ASSIGNMENT OF AN UNDIVIDED;ASSIGNOR:SHARP MICROELECTRONICS TECHNOLOGY, INC.;REEL/FRAME:007806/0395
Effective date: 19960202
|Apr 2, 1999||AS||Assignment|
Owner name: SHARP LABORATORIES OF AMERICA, INC., WASHINGTON
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:SHARP MICROELECTRONICS TECHNOLOGY, INC.;REEL/FRAME:009845/0188
Effective date: 19990330
|Feb 22, 2001||FPAY||Fee payment|
Year of fee payment: 4
|Sep 30, 2004||FPAY||Fee payment|
Year of fee payment: 8
|Mar 2, 2009||FPAY||Fee payment|
Year of fee payment: 12